I have the same issue and also tried restarting the phone via bootloader, which didn't work for me. I got easily into bootloader, but restarting or poweroff followed by normal start always brought me back into "Waiting for flash..." error. I tried it many times and it just didn't work.
But, I found one method which worked for me from pure despair:
1) wait 30 minutes in "waiting screen" - Maybe it's not necessary, but I did it for the first time by coincidence and this method worked. When I didn't wait for some time, the method didn't work...
2) get to bootloader screen (i.e. hold all three buttons and release power and then volume keys only after bootloader menu appears for few seconds) and power off the phone via bootloader menu.
3) wait 5 minutes
4) hold power button for 1-2 seconds to startup as normally until first logo appears, and right after that release power button and start pushing and releasing (i.e. not holding continuously) both volume buttons at once as quickly as possible. Keep "clicking" both volume buttons and the phone should display Qualcomm icon and boot normally.
5) If it doesn't boot normally and ends in Waiting error, restart it via holding power button for a long time and releasing until the first icon appears. Then again as in step #4 release power and keep pushing both volume buttons.
I know the method sounds crazy and probably won't work for many people, but this worked for me three times and allowed me at least to migrate via wifi all data, so maybe it will save also somebody else...
Good luck
